Research ArticleGEOLOGY

A large impact crater beneath Hiawatha Glacier in northwest Greenland

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Science Advances  14 Nov 2018:
Vol. 4, no. 11, eaar8173
DOI: 10.1126/sciadv.aar8173
  • Fig. 1 Geomorphological and glaciological setting of Hiawatha Glacier, northwest Greenland.

    (A) Regional view of northwest Greenland. Inset map shows location relative to whole of Greenland. Magenta box identifies location of (B) to (D). (B) A 5-m ArcticDEM mosaic over eastern Inglefield Land. Colors are ice surface velocity. Blue line illustrates an active basal drainage path inferred from radargrams. (C) Hillshade surface relief based on the ArcticDEM mosaic, which illustrates characteristics such as surface undulations. Dashed red lines are the outlines of the two subglacial paleochannels. Blue lines are catchment outlines, i.e., solid blue line is subglacial and hatched is supraglacial. (D) Bed topography based on airborne radar sounding from 1997 to 2014 NASA data and 2016 Alfred Wegener Institute (AWI) data. Black triangles represent elevated rim picks from the radargrams, and the dark purple circles represent peaks in the central uplift. Hatched red lines are field measurements of the strike of ice-marginal bedrock structures. Black circles show location of the three glaciofluvial sediment samples described in table S1.

  • Fig. 2 Shocked quartz grains from glaciofluvial sediment sample HW21-2016.

    (A to C) Microphotographs and backscattered electron (BSE) microscope images of PDFs. (A) Two sets, symmetrical with respect to the optical and crystallographic c axis. (B) Four sets. (C) Four closely spaced sets throughout a toasted quartz grain. (D) Orientation measurements of 37 sets of PDFs in 10 quartz grains, divided into 2° bins. Reference distribution is for 10 Canadian impact structures with inferred shock pressures >16 GPa (10). (E) Crystallographic indices of 37 PDF sets in 10 shocked quartz grains, with an average of 3.7 measurable sets per grain. (F) Measured quartz PDF orientations in the 10 grains, plotted on a reference net (9). The groups of measurements from each grain were rotated on the c axis to demonstrate an excellent overall three-dimensional (3D) fit with the 350 reference orientations. Only three sets of PDFs could not be indexed in 3D, although they have permissible angles from the c axis.

  • Fig. 3 Impact-related sediment grains from glaciofluvial sediment sample HW21-2016.

    (A) Grain 21C-v32: Pale yellow glass grain of biotite (Bt)–like composition with possibly inherited prismatic sillimanite (Sil) crystals and beginning devitrification in its lower part. (B) 21D-u28: Pale green glass grain of garnet (Grt)–like composition with dark rim and beginning devitrification around small trapped mineral fragments. (C) 21C-t26: Black glass grain of felsic-like composition with new microporphyritic clinopyroxene (Cpx) and ilmenite (Ilm). (D to F) 21B-12a: Microperthitic K-feldspar (Kfs) (D) and brown glass of K-feldspar–like composition (E). Inclusions of quartz (Qtz) have acted as nucleation centers for devitrification (F). (G and H) 21C-z08: Dark brown, ellipsoid glass particle of garnet-like composition with a central contraction crack and beginning crystallization of slender prismatic, radial crystallites. (I and J) 21C-x20: Pale glass grain of aluminous felsic composition with new microporphyritic orthopyroxene (Opx), zoned cordierite (Crd), and skeletal plagioclase (Pl). (K) 21C-u05: Devitrified glass of felsic-like composition with four quartz fragments with PDFs. Arrows indicate prominent PDF orientations. (L) 21C-w29: Pale brown glass of K-feldspar–like composition; quartz inclusion with PDFs (top left) and two round inclusions lined with pale micaceous material, possibly former vesicles in the impact mineral melt. (M) 21C-z22: Lozenge-shaped, toasted quartz fragment with PDFs throughout, rimmed by black amorphous carbonaceous material. (N and O) 21D-r06: Quartz fragment with ballen structure (O), set in a matrix of feldspar-like composition with tiny micaceous crystallites. (P and Q) 21E-p08: Microbreccia with matrix of minute ternary feldspar grains and numerous tiny voids (Q) and inclusions of quartz, K-feldspar, plagioclase, garnet, and ilmenite, and larger elongate, cuspate voids, and channels in quartz (black arrows) with interior linings of clayey material. White arrow in enlargement pointing at a hole from sample preparation, clearly distinguishable from the neighboring original void. (R) 21D-u01: Black ellipsoidal grain comprising numerous target mineral fragments and dust in a carbonaceous matrix identified with scanning electron microscopy–energy-dispersive spectrometry and indicated by microprobe totals of only 40 to 70 wt %. (S) The entire 21D-u01 grain with hole from polishing.

  • Fig. 4 Raman spectra of glassy matrix of selected grains.

    Spectra from three grains shown in Fig. 3, with labeled band peaks.

  • Fig. 5 Radiostratigraphy of Hiawatha Glacier.

    (A and B) Example radargrams across Hiawatha Glacier. See movie S1 for all radargrams. The radargram in (A) passes through the subglacial troughs that enter the crater, so the rim there has been fully eroded. (C) Map of study area showing location of (A) and (B) overlain on local bed topography. (D to G) Examples of mapped radiostratigraphic units within Hiawatha Glacier with key features labeled. (H to J) Thickness of Holocene, LGP, and basal ice within and near Hiawatha Glacier. Background is a natural-color composite Landsat-8 scene from 11 August 2015. Black lines are survey tracks. Units are mapped only where identification is unambiguous. Holocene ice thins as ice flows toward the glacier and is extensively exposed at the ice margin. The incomplete LGP ice sequence thins significantly downstream of the center of the Hiawatha impact crater. Conversely, the apparently debris-rich basal ice thickens significantly downstream of the structure’s center. Inset panels show mean, SD, and distribution of the absolute value of crossover thickness differences.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/11/eaar8173/DC1

    Supplementary Text

    Fig. S1. Bedrock type and lineations across Inglefield Land near Hiawatha Glacier.

    Fig. S2. Terminus history of Hiawatha Glacier and its transition from a floating to a grounded tongue with a proglacial floodplain.

    Fig. S3. CI-chondrite–normalized metal patterns for glaciofluvial sediment samples compared to upper continental crust.

    Fig. S4. Model mixtures of crust with mass proportions of various meteorites.

    Fig. S5. Radar reflectivity at the six deep Greenland ice-core sites, as measured by predecessor radar systems to that used for the Hiawatha Glacier survey.

    Fig. S6. Relationships between surface and radar layering.

    Fig. S7. Supraglacial drainage of Hiawatha Glacier.

    Table S1. Location and description of Hiawatha glaciofluvial sediment samples.

    Movie S1. The 2016 AWI airborne radar survey over Hiawatha Glacier.

    Movie S2. Operation IceBridge radar surveys across the Greenland Ice Sheet.

    Movie S3. Operation IceBridge radar surveys toward Hiawatha Glacier.

    Data file S1. EMP data for grains studied from HW21-2016 samples.

    Data file S2. Major element, trace element, and PGE concentrations for subsamples and sub-subsamples of HW21-2016.

    References (4144)

  • Supplementary Materials

    The PDF file includes:

    • Supplementary Text
    • Fig. S1. Bedrock type and lineations across Inglefield Land near Hiawatha Glacier.
    • Fig. S2. Terminus history of Hiawatha Glacier and its transition from a floating to a grounded tongue with a proglacial floodplain.
    • Fig. S3. CI-chondrite–normalized metal patterns for glaciofluvial sediment samples compared to upper continental crust.
    • Fig. S4. Model mixtures of crust with mass proportions of various meteorites.
    • Fig. S5. Radar reflectivity at the six deep Greenland ice-core sites, as measured by predecessor radar systems to that used for the Hiawatha Glacier survey.
    • Fig. S6. Relationships between surface and radar layering.
    • Fig. S7. Supraglacial drainage of Hiawatha Glacier.
    • Table S1. Location and description of Hiawatha glaciofluvial sediment samples.
    • Legends for Movies S1 to S3
    • Legends for Data files S1 and S2
    • References (4144)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). The 2016 AWI airborne radar survey over Hiawatha Glacier.
    • Movie S2 (.mp4 format). Operation IceBridge radar surveys across the Greenland Ice Sheet.
    • Movie S3 (.mp4 format). Operation IceBridge radar surveys toward Hiawatha Glacier.
    • Data file S1 (Microsoft Excel format). EMP data for grains studied from HW21-2016 samples.
    • Data file S2 (Microsoft Excel format). Major element, trace element, and PGE concentrations for subsamples and sub-subsamples of HW21-2016.

    Files in this Data Supplement:

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